1. Field of the Invention
The present invention relates to an X-ray tube and an X-ray analysis apparatus for use, for example, in an energy-dispersive X-ray fluorescent spectrometer. The X-ray tube and X-ray analysis apparatus are preferably used as small-sized, lightweight, handy or portable apparatus.
2. Description of the Related Art
Fluorescent X-ray analysis is used to perform qualitative or quantitative analysis of a sample by directing primary X-rays emanating from an X-ray source at the sample, detecting fluorescent X-rays released from the sample by an X-ray detector, and obtaining a spectrum from the energies of the fluorescent X-rays. The fluorescent X-ray analysis makes it possible to analyze the sample non-destructively and quickly and, therefore, enjoys wide acceptance in manufacturing process management and quality control.
One analytical method of the fluorescent X-ray analysis is wavelength-dispersive spectrometry in which fluorescent X-rays are spectrally resolved by an analyzing crystal and the wavelengths and intensities of the X-rays are measured. Another analytical method of the fluorescent X-ray analysis is energy-dispersive X-ray spectrometry in which fluorescent X-rays are detected by a semiconductor detector device without spectrally dispersing the X-rays and the energies and intensities of the X-rays are measured by a pulse height analyzer.
A conventional attempt to enhance the sensitivity for fluorescent X-rays is described, for example, in JP-A-8-115694. An X-ray tube is provided with a window to permit fluorescent X-rays passing into the tube to be taken out. The X-ray tube and X-ray analyzer are brought closer to the sample.
As described in Japanese Patent No. 3,062,685, handy energy-dispersive fluorescent X-ray analysis apparatus have become widespread owing to reductions in size of X-ray tubes and X-ray analyzers.
The above-described conventional techniques have the following problems. For example, in the X-ray analysis apparatus described in patent reference 1, the detection sensitivity is effectively enhanced by bringing the X-ray tube and X-ray analyzer closer to the sample. However, the X-ray tube and X-ray analyzer are finite in size and have dimensions greater than given values. Therefore, it has been impossible to bring the X-ray tube and X-ray analyzer infinitely close to the sample.
Furthermore, there is a demand for further reductions in size and weight of conventional handy energy-dispersive fluorescent X-ray analyzers. Because the X-ray tube and X-ray analyzer together occupy the greater parts of the volume and mass of the instrument, restrictions are imposed on further reductions in size and weight if the conventional form is reserved. In addition, in the handy type, a sample to be analyzed is not held in a closed sample chamber. Rather, a sample within the atmosphere is directly irradiated with primary X-rays. That is, the instrument is of open type. Consequently, for safety reasons, the amount of X-rays produced from the X-ray tube is limited. Consequently, it has been necessary to detect fluorescent X-rays from the sample more efficiently.